Oxidative Breaking of Long-Chain Acetylenic Enol Ethers of Glycerol of the Marine Sponges Raspailia pumila and of Model Compounds with Aerial Oxygen

✍ Scribed by Graziano Guella; Ines Mancini; Francesco Pietra

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: German
• Weight: 745 KB
• Volume: 70
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19870700521

✦ Synopsis

The raspailynes (novel long-chain enol cthcrs of glycerol having the enol ether double bond conjugated, in sequence, to an acetylenic and an olefinic bond, isolated from the North-East-Atlantic sponges Raspilia prtmila and R.rumo.sa) are stable under normal hydrolytic conditions for enol ethers. In contrast, when their solutions are evaporated, these lipids such as raspailyne BI ( = (-)-3-[( IZ,5Z)-(tetradeca-1,5-dien-3-ynyl)oxy]-1,2-propanediol; (-)-2) rapidly react with aerial 0, under normal laboratory-daylight conditions, with rupture of the C=C enol ether bond to give 1-0-formylglycerol(3) and an aldehyde (such as tridec-4-en-2-ynal( 4) from (-)-2). This reaction must be caused by triplet O,, since thermally gcnerated singlet 0, has no efTect on (-)-2 in solution. That the mere presence of an enol-ether moiety conjugated to an acetylenic group is responsible for such a behaviour is demonstrated with the model compounds l-methoxypentadec-l-en-3-yn-5-01(6a) and its 5-0-acetyl or 5-0-tetrahydropyranyl derivatives 6b and 6c, respectively. Resistance to both hydrolytic conditions and singlet 0, of' these compounds is thought to arise from electron depletion at the enol-ether C(B) atom by the acetylenic group. Plausible reaction pathways for enol-ether bond rupture in these compounds by aerial 0, are outlined.

') This also contrasts with the behaviour of natural polyolefinic glycerol vinyl ethers such as the fecapentaenes.

These are mutagenic compounds of bacterial origin, isolated from human feces [4a]. which decompose rapidly in the presence of aqueous acids [4b], whilst they behave as electrophiles under acidic conditions in anhydrous dimethyl sulfoxide [k].